1. Field of the Invention:
The present invention generally relates to a system for the detection of the shift position selected in a motor vehicle transmission.
2. Background Information:
For a number of applications, e.g. in an automatic friction clutch in the drive train of a motor vehicle, or damping force control systems on the chassis of a motor vehicle, a knowledge of the instantaneous gear or shift position which has been selected in a multispeed transmission is necessary to achieve the most comfortable ride possible, or to perform control procedures which may be necessary for vehicle safety. In particular, not only is it desirable to detect the intention to shift gears as early as possible, i.e. to identify the shift position of the transmission, but the system should also be capable of detecting, as early as possible, which gear is being shifted into.
DE-A-38 36 145 discloses a method which employs a flat potentiometer, the movable wiper of which can be moved over a flat resistance in two coordinate directions and is coupled to a manually actuated shift lever of the transmission, which makes it possible to detect the instantaneous position to which the transmission is being shifted. An evaluation circuit measures the resistance ratios determined by the shift position of the transmission in the two coordinate directions, and assigns the measured resistance ratios to value ranges which are specified for the individual shift positions. The value ranges are defined in a learning process on the basis of the current design, which of course makes the calibration of the system easier, but requires relatively expensive circuitry. The flat potentiometer is also relatively complex and expensive, and is susceptible to malfunctions.
DE-A-42 08 888 discloses a system for the detection of the shift position of a motor vehicle transmission by means of a switch module which is attached to the housing of the transmission. The switch module contains a number of magnetic field sensors which respond to magnets, which magnets are located on the sliding selector shafts of the transmission. The selector shafts change the pairs of gear wheels. The magnetic field sensors are arranged so that they respond to the magnets in the limit positions of the sliding selector shafts. From the combination of magnetic field sensors actuated, an evaluation circuit can then be used to identify the instantaneous shifting position selected in the transmission. In addition to the fact that a comparatively large number of such magnetic field sensors are required in a conventional multispeed transmission of a motor vehicle, the calibration of the magnetic field sensors can present problems.
In particular, in automatic friction clutches of motor vehicles, the clutch control should be informed of the intention to shift gears. The transmission can be shifted by means of motorized actuators, in which case the signals indicating an upcoming change of gear are supplied by the transmission control system. For transmissions which are shifted manually, there are known devices which include a switch in the shifting mechanism, which, in this case, is represented by a shift lever. The displacement of the shift lever which initiates the shifting of the transmission actuates this switch. Such a shift lever sensor is disclosed in DE-A-42 37 669, for example. This shift lever sensor is integrated into the handle of the shift lever, and comprises two switch contacts. These switch contacts can make it possible to identify the direction of movement of the shift lever.